An organic electroluminescent element includes a first electrode disposed on a substrate, an organic compound layer including a light-emitting layer, and a second electrode, which are stacked on top of each other. Improvement in the luminous efficiency is required for organic electroluminescent elements. To address this issue, PTL 1 describes an organic electroluminescent element that achieves a high efficiency by having an organic capping layer stacked in an upper part of the organic electroluminescent element.
Organic electroluminescent elements are prone to corrosion and oxidation. Therefore, it is necessary to seal organic electroluminescent elements. Sealing configurations are classified into two types. In one type of configuration, an organic electroluminescent element is filled with dry air and sealed with a sealing cap. In the other type of configuration, an organic electroluminescent element is covered with a protective layer that is not permeable to water and oxygen. PTL 2 describes an organic electroluminescent element that is covered with a protective layer made of silicon oxynitride (SiON)/organic material/silicon oxynitride (SiON).
When the sealing configuration with the protective layer is used in the organic electroluminescent element described in PTL 1, in which an organic capping layer is stacked in the upper part of the organic electroluminescent element, the difference in the refractive indices at the interface between the organic capping layer and the protective layer is not large. Therefore, it is difficult to produce an effect described in PTL 1 when the sealing configuration with the protective layer is used.